Oxidation catalysts and process for preparing anhydride from alkanes

ABSTRACT

A catalyst complex useful for the partial oxidation of alkanes to the corresponding anhydrides, e.g., converting normal C 4  hydrocarbons to maleic anhydride in vapor phase, comprising as components vanadium, phosphorus, oxygen, Cu, Mo, Ni, Co, Cr, Nd, Ce, Ba, Y and Sm.

This is a division of application Ser. No. 793,752, filed May 4, 1977.

BACKGROUND OF THE INVENTION

The present invention relates to an improved process for the preparationof dicarboxylic anhydride from C₄ -C₁₀ hydrocarbons preferably using afeed containing major amounts of alkanes, by the reaction of oxygen withthe hydrocarbon in vapor phase over a particular novel catalyst, such asthe preparation of maleic anhydride from butane.

The production of dicarboxylic acid anhydride by catalytic oxidation ofhydrocarbons is well known. The current principal route for theproduction of maleic anhydride from C₄ hydrocarbons has been desirablein the past, but is now even more desirable in view of the particularworld shortage of benzene. It can be readily appreciated that directoxidation of C₄ hydrocarbons would be a hydrocarbon conservation, sincefor each mol of maleic anhydride prepared from benzene, one mol ofbenzene, molecular weight 78 is consumed, whereas for each mol of theC₄, only 54 to 58 mol weight of hydrocarbon is consumed. The benzeneprocess has consistently produced high conversions and selectivities.Although processes for the oxidation of aliphatic hydrocarbons arereported in the literature, there are certain defects and inadequaciesin these processes, such as short catalyst life and low yields ofproduct. Furthermore, although many of the prior art methods aregenerically directed to "aliphatic" hydrocarbons, they are in allpractical aspects directed to unsaturated aliphatic hydrocarbons.

A more desirable process for producing maleic anhydride would be adirect oxidation of n-butane. There are several advantages. Principalamong these is the greater availability of n-butane as compared ton-butenes or butadiene. Also, n-butenes may be higher economicpetrochemical utilization than the n-butanes, which are now, oftenwastefully burned as cheap fuel.

In an early series of patents, Ralph O. Kerr developed a unique group ofvanadium-phosphorus, oxidation catalysts, i.e., U.S. Pat. Nos.3,156,705; 3,156,706; 3,255,211; 3,255,212; 3,255,213; 3,288,721;3,351,565; 3,366,648; 3,385,796 and 3,484,384. These processes andcatalysts proved highly efficient in the oxidation of n-butenes tomaleic anhydride. Since the issuance of these pioneer patents, numerouspatents have issued with various modifications and improvements over thebasic discoveries set forth there, e.g., U.S. Pat. Nos. 3,856,824;3,862,146; 3,864,280, 3,867,411 and 3,888,886.

Most recently, Kerr discovered that vanadium-phosphorus-oxygen complextype catalyst modified with a particular group of components is anexcellent oxidation catalyst for the conversion of C₄ to C₁₀hydrocarbons to the corresponding anhydrides, particularly, n-C₄hydrocarbons to maleic anhydride, which is disclosed and claimed incommonly assigned U.S. Pat. Application Ser. No. 767,499, filed Feb. 10,1977. In addition to n-butane, n-butene and butadiene may also be usedas feeds. The catalyst contained only a minor amount of the modifyingcomponent. The essential elements of the modifying component weredetermined by Kerr to be Nb, Cu, Mo, Ni, Co and Cr. In addition to theessential elements, the modifying component may contain one or moreelements from the group consisting of Y, Sm, Tb and Eu, i.e., avanadium-phosphorus-oxygen complex type catalyst for the conversion ofC₄ to C₁₀ hydrocarbons to the corresponding anhydrides in which thecatalyst contains the essential modifying elements of Nb, Cu, Mo, Ni, Coand Cr, and one or more of the elements selected from the groupconsisting of Y, Sm, Tb and Eu. In addition to these modifiers, the Kerrcatalyst might also contain one or more of the elements from the groupconsisting of Ce, Nd, Ba, Hf, U, Ru, Re, Li or Mg.

SUMMARY OF THE INVENTION

The present inventor has surprisingly found that the omission of Nb froma specific prior catalyst of Kerr, not only did not result in anyadverse effect, but was beneficial in producing unexpected improvementin the catalyst operation, i.e., better yields under the same or morefavorable conditions of maleic ahydride production.

Hence, briefly stated, the present invention is avanadium-phosphorus-oxygen complex type catalyst for the conversion ofhydrocarbons to the corresponding anhydrides in which the catalystcontains the essential modifying elements of Cu, Mo, Ni, Co, Cr, Nd, Ce,Ba, Y and Sm.

The precise structure of the present complex catalyst has not beendetermined; however, the complex may be represented by formula

    VP.sub.a Me.sub.b O.sub.x

wherein Me is the modifying component described above, a is 0.90 to 1.3,b is at least 0.033 to 0.4. The representation is not an empiricalformula and has no significance other than representing the atom ratioof the active metal components of the catalyst. The x, in fact, has nodeterminate value and can vary widely, depending on the combinationswithin the complex. That there is oxygen present is known and the O_(x)is representative of this.

The following listing shows the ranges of each member of the complex,including the modifying component. The relative proportions are shown inatomic ratio relative to vanadium which is designated as 1. The amountsof components are selected within these ranges so that the total atomsof modifying component stays within the range given above, i.e., atleast 0.033 to 0.4 atom per atoms of vanadium.

    ______________________________________                                        Catalyst           Atomic                                                     Component          Ratio                                                      ______________________________________                                        V                    1                                                        P                  0.90-1.3                                                   Cu                 0.022-0.201                                                Mo                 0.0025-0.040                                               Ni                 0.0022-0.045                                               Co                 0.0040-0.066                                               Ce                 0.0054-0.20                                                Nd                 0.0022-0.20                                                Cr                 0.0003-0.003                                               Ba                 0.0023-0.0585                                              Y                  0.0001-0.02                                                Sm                 0.0001-0.02                                                ______________________________________                                    

The oxygen atomic ratio may vary widely, generally in the range of 5 to8, for the catalyst composition of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The catalyst may be prepared in a number of ways. The catalyst may beprepared by dissolving compounds of vanadium, phosphorus and othercompound components, i.e., Cu, Mo, Ni, Co, Ce, Nd, Cr, Ba, Y or Sm in acommon solvent, such as hot hydrochloric acid and thereafter depositingthe solution onto a carrier. The catalyst may also be prepared byprecipitating the various compounds, either with or without a carrierfrom a colloidal dispersion of the ingredients in an inert liquid. Insome instances, the catalyst may be deposited as molten compounds onto acarrier; however, care must be taken not to vaporize off any of theingredients such as phosphorus. The catalyst may also be prepared byheating and mixing anhydrous forms of phosphorus acids with vanadiumcompounds and compounds of the other components. The catalyst may beused as either fluid bed or fixed bed catalysts. In any of the methodsof preparation, heat may be applied to accelerate the formation of thecomplex.

According to one solution method, the vanadium is present in solutionwith an average valence of less than plus 5 in the finally formedcomplex in solution. Preferably, the vanadium has an average valency ofless than plus 5 at the time the solution of catalyst complex isdeposited onto the carrier, if a carrier is used. The reduced vanadiumwith a valence of less than 5 may be obtained either by initially usinga vanadium compound wherein the vanadium has a valence of less than 5,such as vanadyl chloride, or by initially using a vanadium compound witha valence of plus 5, such as V₂ O₅, and thereafter reducing to the lowervalence with, for example, hydrochloric acid during the catalystpreparation to form the vanadium oxysalt, vanadyl chloride, in situ. Thevanadium compound may be dissolved in a reducing solvent, such ashydrochloric acid, which solvent functions not only to form a solventfor the reaction, but also to reduce the valence of the vanadiumcompound to a valence of less than 5. Preferably, the vanadium compoundis first dissolved in the solvent and thereafter the phosphorus andother metal (metalloid) compounds are added. The reaction to form thecomplex may be accelerated by the application of heat. The deep bluecolor of the solution shows the vanadium has an average valence of lessthan 5. The complex formed is then dried to a solid. In this procedure,the vanadium has an average valence of less than plus 5, such as aboutplus 4. Generally, the average valence of the vanadium will be betweenabout plus 2.5 and 4.6 at the time of deposition onto the carrier.

When the above described solution method is employed, reducing agentsfor the vanadium may be either organic or inorganic. Acids such ashydrochloric, hydroiodic, hydrobromic, acetic, oxalic, malic, citric,formic and mixtures thereof, such as a mixture of hydrochloric andoxalic may be used. Sulfur dioxide may be used. Less desirably, sulfuricand hydrofluoric acids may be employed. Other reducing agents which maybe employed, but which have not been given as desirable catalysts areorganic aldehydes such as formaldehyde and acetaldehyde; alcohols suchas pentaerythritol, diacetone alcohol and diethanol amine. Additionalreducing agents are such as hydroxyl amines, hydrazine and nitric oxide.Nitric acid and similar oxidizing acids which would oxidize the vanadiumfrom a valence of 4 to 5 during the preparation of the catalyst shouldbe avoided. Generally, the reducing agents form oxysalts of vanadium.For example, if V₂ O₅ is dissolved in hydrochloric or oxalic acid, thecorresponding vanadium oxysalts are produced. These vanadium oxysaltsshould have as the salt forming anion, an anion which is more volatilethan the phosphate anion.

Any vanadium, phosphorus and metal and metalloid compounds may be usedas starting materials which, when the compounds are combined and heatedto dryness in air at a temperature of, for example, 300°-350° C. willleave as a deposit a catalyst complex having relative proportions withinthe described ranges. In the solution methods, preferred are vanadium,phosphorus and metal and metalloid compounds, which are essentiallycompletely soluble in boiling aqueous hydrochloric acid at 760 mm. ofmercury, containing 37 percent by weight hydrochloric acid. Generally,phosphorus compounds are used which have as the cation an ion which ismore volatile than the phosphate anion, for example, H₃ PO₄. Also,generally any vanadium or Me compound which has as an anion, an anionwhich is either the phosphate ion or an ion which is more volatile thanthe phosphate anion, for example, vanadyl chloride or copper chloride,nickel chloride or the like, may be used.

In another method, a solution of the vanadium component is prepared byadding a portion of a reducing agent, such as oxalic acid andisopropanol solution to a solution of water and phosphoric acid, andheating this mixture to a temperature, generally of around 50°-80° C. Avanadium compound such as V₂ O₅ is added incrementally to this heatedmixture with stirring. The blue solution which indicates vanadium ofaverage valency less than 5, is maintained by adding increments of theremaining oxalic acid-isopropanol solution. After concentration of thissolution, solutions of other components are added to vanadium solutionand this resultant solution concentrated to a paste-like consistency,heated at moderate temperature, i.e., 200°-400° C. for a few minutes toseveral hours and prepared in pellets or chips.

As the source of phosphorus, various phosphorus compounds may be used,such as metaphosphoric acid, triphosphoric acid, pyrophosphoric acid,ortho-phosphoric acid, phosphorus pentoxide, phosphorus oxyiodide, ethylphosphate, methyl phosphate, amine phosphate, phosphorus pentachloride,phosphorus trichloride, phosphorus oxybromide and the like.

Suitable vanadium compounds useful as starting materials are compoundssuch as vanadium pentoxide, ammonium metavanadate, vanadium trioxide,vanadyl chloride, vanadyl dichloride, vanadyl trichloride, vanadiumsulfate, vanadium phosphate, vanadium tribromide, vanadyl formate,vanadyl oxalate, metavanadic acid, pyrovanadic acid, and the like.Mixtures of the various vanadium, phosphorus and metal and metalloidcompounds may be used as starting materials to form the describedcatalyst complex.

The metal or metalloid component is also suitably introduced byemploying the various compounds thereof such as the acetates,carbonates, chlorides, bromides, oxides, hydroxides, nitrates,chromates, chromites, tellurates, sulfides, phosphates, and the like.The compounds are entirely conventional and those of ordinary skill inthe art know these materials and can readily determine suitablecompounds to prepare the catalyst, with little, if any, experimentation.A few illustrative compounds are nickel chloride, chromium sulfate,chromium trioxide, chromium chloride, barium chloride and similarcompounds.

A catalyst support, if used, provides not only the required surface forthe catalyst, but gives physical strength and stability to the catalystmaterial. The carrier or support normally has a low surface area, asusually measured from about .110 to about 5 square meters per gram. Adesirable form of carrier is one which has a dense non-absorbing centerand a rough enough surface to aid in retaining the catalyst adheredthereto during handling and under reaction conditions. The carrier mayvary in size, but generally is from about 21/2 mesh to about 10 mesh inthe Tyler Standard screen size. Alundum particles as large as 1/4 inchare satisfactory. Carriers much smaller than 10 to 12 mesh normallycause an undesirable pressure drop in the reactor, unless the catalystsare being used in a fluid bed apparatus. Very useful carriers areAlundum and silicon carbide or Carborundum. Any of the Alundums or otherinert alumina carriers of low surface may be used. Likewise, a varietyof silicon carbides may be employed. Silica gel may be used.

The amount of the catalyst complex on the carrier is usually in therange of about 15 to about 95 weight percent of the total weight ofcomplex plus carrier and preferably in the range of 50 to 90 weightpercent and more preferably at least 60 weight percent on the carrier.The amount of the catalyst complex deposited on the carrier should beenough to substantially coat the surface of the carrier and thisnormally is obtained with the ranges set forth above. With moreabsorbent carriers, larger amounts of material will be required toobtain essentially complete coverage of the carrier. In a fixed bedprocess, the final particle size of the catalyst particles which arecoated on a carrier will also preferably be about 21/2 to about 10 meshsize. The carriers may be of a variety of shapes, the preferred shape ofthe carriers is in the shape of cylinder or spheres. Although moreeconomical use of the catalyst on a carrier in fixed beds is obtained,as has been mentioned, the catalyst may be employed in fluid bedsystems. Of course, the particle size of the catalyst used in fluidizedbeds is quite small, usually varying from about 10 to about 150 microns,and in such systems, the catalyst normally will not be provided with acarrier, but will be formed into the desired particle size after dryingfrom solution.

Inert diluents may be present in the catalyst, but the combined weightof the active ingredients, e.g., vanadium, oxygen, phosphorus, metal andmetalloid should preferably consist essentially of at least about 50weight percent of the composition which is coated on the carrier, ifany, and preferably these components are at least about 75 weightpercent of the composition coated on the carrier, and more preferably,at least about 95 weight percent.

In one procedure for preparing the present catalyst compositions, thevanadium component is prepared by adding a portion of a reducing agent,such as an oxalic acid with or without isopropanol, to a solution ofwater and phosphoric acid and heating this mixture to a temperaturegenerally around 50°-60° C. A vanadium compound, such as V₂ O₅ is slowlyadded while raising the temperature of the solution to 60°-90° C. A bluesolution indicates vanadium of average valency of less than 5 at whichtime the molybdenum component as MoO₃ is added to the solution anddissolved therein. The remainder of the catalyst components are added tothis mixture as solutions, preferably of the chloride salts, e.g.,obtained by dissolving oxides and/or carbonates in HCl.

Thus, this method of catalyst preparation involves two particularaspects. First, the vanadium is reduced with a reducing agent in asolution containing phosphoric acid and a second, a majority (over 50%by component) of the remaining catalyst components are employed as thechloride salts. In particular, Ni, Co, Cu, Cr, Nd, Ce, Ba, Y and Sm, areemployed as chloride salts. All of the metal and metalloid elementsemployed in preparing the catalyst, with the exception of vanadium andphosphorus, may be used as the chloride salt.

The resulting mixture is dried at 85°-135° C. and broken into pieces of4 to 20 mesh and dried further at 120°-130° C., then heated at 300° C.for an additional period of 0.5 to two or three hours. The catalyst maybe used as such, but is preferably reduced to a powder and pelleted. Asnoted above, binders, such as stearic acid, carriers and inert fillersmay be added before pelleting.

The oxidation of the n-C₄ hydrocarbon to maleic anhydride may beaccomplished by contacting, e.g., n-butane, in low concentrations inoxygen with the described catalyst. Air is entirely satisfactory as asource of oxygen, but synthetic mixtures of oxygen and diluent gases,such as nitrogen, also may be employed. Air, enriched with oxygen may beemployed.

The gaseous feed stream to the oxidation reactors normally will containair and about 0.5 to about 2.5 mol percent hydrocarbons, such asn-butane. About 1.0 to about 1.7 mol percent of the n-C₄ hydrocarbonsare satisfactory for optimum yield of product for the process of thisinvention. Although higher concentrations may be employed, explosivehazards may be encountered. Lower concentrations of C₄, less than aboutone percent, of course, will reduce the total yields obtained atequivalent flow rates and thus, are not normally economically employed.The flow rate of the gaseous stream through the reactor may be variedwithin rather wide limits, but a preferred range of operations is at therate of about 50 to 300 grams of C₄ per liter of catalyst per hour andmore preferably, about 100 to about 250 grams of C₄ per liter ofcatalyst per hour. Residence times of the gas stream will normally beless than about 4 seconds, more preferably less than about one second,and down to a rate where less efficient operations are obtained. Theflow rates and residence times are calculated at standard conditions of760 mm. of mercury and at 25° C. An improved output of maleic anhydridecan be obtained with various catalysts of the present invention, if thefeed consists essentially of C₄ normal alkane, i.e., about comprising 88to 99 or more weight percent normal C₄ alkane, and from about 1 to 12weight percent n-butene, benzene, or a mixture thereof. A preferred feedfor the catalyst of the present invention for conversion to maleicanhydride is a n-C₄ hydrocarbon comprising a predominant amount ofn-butane and more preferably, at least 90 mol percent n-butane.

A variety of reactors will be found to be useful and multiple tube heatexchanger type reactors are quite satisfactory. The tubes of suchreactors may vary in diameter from about 1/4 inch to about 3 inches, andthe length may be varied from about 3 to about 10 or more feet, e.g., 12feet. The oxidation reaction is an exothermic reaction and, therefore,relatively close control of the reaction temperature should bemaintained. It is desirable to have the surface of the reactors at arelatively constant temperature and some medium to conduct heat from thereactors is necessary to aid temperature control. Such media may beWoods metal, molten sulfur, mercury, molten lead, and the like, but ithas been found that eutectic salt baths are completely satisfactory. Onesuch salt bath is a sodium nitrate-sodium nitrate-potassium nitrateeutectic constant temperature mixture. An additional method oftemperature control in the laboratory is to use a metal block reactor,whereby the metal surrounding the tube acts as a temperature regulatingbody. As will be recognized by those skilled in the art, the heatexchange medium may be kept at the proper temperature by heat exchangersand the like. The reactor or reaction tubes may be iron, stainlesssteel, carbon steel, nickel, glass tubes, such as Vycor, and the like.Both carbon steel and nickel tubes have excellent long life under theconditions of the reactions described herein. Normally, the reactorscontain a preheat zone of an inert material such as 1/4 inch Alundumpellets, inert ceramic balls, nickel balls or chips and the like,present at about one-half to one-tenth the volume of the active catalystpresent.

The temperature of reaction may be varied within some limits, butnormally, the reaction should be conducted at temperatures within arather critical range. The oxidation reaction is exothermic and oncereaction is underway, the main purpose of the salt bath or other mediais to conduct heat away from the walls of the reactor and control thereaction. Better operations are normally obtained when the peak reactiontemperature employed is no greater than about 100° C. above the saltbath temperature. The temperature in the reactor, of course, will alsodepend to some extent upon the size of the reactor and the C₄concentration. Under usual operating conditions, in compliance with thepreferred procedure of this invention, the temperature in the center ofthe reactor, measured by thermocouple, is about 375° C. to 550° C. Therange of temperature preferably employed in the reactor, measured asabove, should be from about 390° C. to about 460° C., and the bestresults are ordinarily obtained at temperatures from about 410° C. toabout 450° C.

Described another way, in terms of salt bath reactors with carbon steelreactor tubes about 1.0 inch in diameter, the salt bath temperature willusually be controlled between about 350° C. to about 450° C. Undernormal conditions, the temperature in the reactor ordinarily should notbe allowed to go above about 450° C. for extended lengths of timebecause of decreased yields and possible deactivation of the novelcatalyst of this invention.

The reaction may be conducted at atmospheric, super-atmospheric orbelow-atmospheric pressure. The exit pressure will be at least slightlyhigher than the ambient pressure to insure a positive flow from thereaction. The pressure of the inert gases may be sufficiently high toovercome the pressure drop through the reactor.

In one utilization of the present catalyst compositions, the oxidationis carried out at 15 to 100 psig, preferably about 20 to 50 psig, andmore preferably about 25 to 40 psig.

Operating under pressure as described above, the temperature in thecenter of the reactor, measured by thermocouple is about 375° C. toabout 550° C. with the preferred temperature range for operatingaccording to the present invention being 430° C. to 480° C., and thebest results are ordinarily obtained at temperatures from about 430° C.to about 455° C. Described another way, in terms of salt bath reactorswith carbon steel reactor tubes about 1.0 inch in diameter, the saltbath temperature will usually be controlled between about 325° C. toabout 440° C. Under these conditions, the temperature in the reactorordinarily should not be allowed to go above about 450° C. for extendedlengths of time because of decreased yields and possible deactivation ofthe novel catalyst of this invention.

The maleic anhydride may be recovered by a number of ways well known tothose skilled in the art. For example, the recovery may be by adsorptionin suitable media, with subsequent separation and purification of themaleic anhydride.

In the following examples, percents are by weight unless otherwisespecified.

EXAMPLES 1, 2, 3 and 4 Reactor

The salt bath reactor used to evaluate the catalyst compositionsemployed 3/16" catalyst pellets in a 12 foot by 11/4 inch fixed bed ofcatalyst packed in a carbon steel tube, with inert 1/4 inch Alundumpellets on top of the catalyst material to a height 1/3 of the height ofthe catalyst.

The reactors were encased in a 7% sodium nitrate-40% sodium nitrite-53%potassium nitrate eutectic mixture constant temperature salt bath. Thereactor was slowly warmed to 400° C. (250°-270° C. air passing overcatalyst) while passing a gas stream containing 0.5 to 0.7 mol percentn-butane and air over the catalyst beginning at about 280° C. Thereactor outlet was maintained at 1 psig. After the reactor had reached390° C., the catalyst was aged by passing the n-butane-air mixturetherethrough for 24 hours. The n-butane-air and temperature wasincreased to obtain a maximum throughput. The n-butane in the feed isincreased to 1.0-1.5 mol percent to obtain 70-80% conversion. The saltbath is operated at a maximum of 420° C. The maximum throughput isachieved in relation to the maximum salt bath temperature and a maximumhot spot of about 450° C. The hot spot is determined by a probe throughthe center of the catalyst bed. The temperature of the salt bath can beadjusted to achieve the desired relationship between the conversion andflow rates of the n-C₄ -air mixture. The flow rate is adjusted to about75% conversion and the temperature relations given above. Generally,flow rates of about 70 to 120 grams of hydrocarbon feed per liter hourare used. The exit gases were cooled to about 55-60° C. at about 1/2psig. Under these conditions, about 30-50% of the maleic anhydridecondenses out of the gas stream. A water scrubber recovery andsubsequent dehydration and fractionation were used to recover and purifythe remaining maleic anhydride in the gas stream after condensation. Thecombined maleic anhydride recovered is purified and recovered at atemperature of about 140°-165° C. overhead and 165° C. bottomstemperatures in a fractionator. The purified product had a purity of99.9+ percent maleic anhydride.

    ______________________________________                                        Catalyst Preparation                                                          Catalyst A Contains Nb                                                                          Catalyst B, No Nb                                           ______________________________________                                        Ingredients:          Ingredients:                                            V.sub.2 O.sub.5                                                                          1222.459 g V.sub.2 O.sub.5                                                                            1222.459 g                                 MoO.sub.3  24.25  g   MoO.sub.3    24.25  g                                   CuCl.sub.2 . 2H.sub.2 O                                                                  206.002 g  CuCl.sub.2 . 2H.sub.2 O                                                                    206.002 g                                  NiO        17.524 g   NiO          17.524 g                                   CoCl.sub.2 . 6H.sub.2 O                                                                  71.726 g   CoCl.sub.2 . 6H.sub.2 O                                                                    71.726 g                                   CrO.sub.3  2.425 g    CrO.sub.3    2.425 g                                    BaCl.sub.2 . 2H.sub.2 O                                                                  38.632 g   BaCl.sub.2 . 2H.sub.2 O                                                                    38.632 g                                   CeO.sub.2  50.0  g    CeO.sub.2    50.0  g                                    Nd.sub.2 O.sub.3                                                                         25.0  g    Nd.sub.2 O.sub.3                                                                           25.0  g                                    Y.sub.2 O.sub.3                                                                          6.566 g    Y.sub.2 O.sub.3                                                                            6.566 g                                    Sm.sub.2 O.sub.3                                                                         3.740 g    Sm.sub.2 O.sub.3                                                                           3.740 g                                    Nb.sub.2 O.sub.5                                                                         75.0  g                                                            ______________________________________                                    

Reaction Mixture Catalyst A

Heat the mixture to 50°-60° C. and add the V₂ O₅ slowly while raisingthe temperature to 65° C. to 85° C. After all of the V₂ O₅ is added,reflux slowly until the solution is homogeneous and blue. Reduce thevolume to 6000 ml. by taking off water and alcohol on reflux. Add theMoO₃ to the vanadyl phosphate solution and continue to reflux and reducethe volume to about 4000 ml. The Nb₂ O₅ is added to a tumbler, about 80liter size, and prewarmed to 40°-60° C. The concentrated V-P-Mo mixtureis then added to the tumbler. The heat source is increased to raise thetemperatures to 75°-90° C. and held there. The NiO is dissolved in 1600ml. of HCl along with the CoCl₂.6H₂ O. The oxides are digested to thesoluble chlorides while reducing the HCl volume to 800 ml., 400 ml. ofH₂ O is added to the clear, dark solution. The Ni-Co mixture is thenadded to the V-P-Mo-Nb₂ O₅ mixture in the tumbler. The CuCl₂.2H₂ O isdissolved in 1600 ml. of H₂ O and is added next; followed by CrO₃ in 200ml. of H₂ O. When the mixture becomes green and slightly viscous, Nd₂O₃, dissolved in H₂ O and HCl and CeO₂, dissolved in concentrated HCl,are added along with BaCl₂ (if any) in H₂ O, and shortly after this, theY₂ O₃ and Sm₂ O₃ (as appropriate) are added. After heating and loss ofwater vapor, the mixture becomes more viscous and difficult to stir. Itis then transferred to pyrex dishes. The green mixture is dried from 85°C. to 100° to 135° C. over a 36-hour period. The solid mass is broken upto a 4 mesh, or less, and dried from 120 to 300° C. over 4 hours; heldat 300° C. for one hour. The chipped catalyst is ball-milled in a dryatmosphere for 6 hours to obtain 60 mesh fines. To this is mixed 0.5%Curtin type graphite and 1% Baker stearic acid. 3/16"×3/16" pellets areproduced. The pellets are heated slowly to 300° C. so that they can beadded directly to the hot salt reactor held at 250° C.

The conditions of the reactors and results of maleic anhydridepreparation from n-butane are set out below in Table I.

Catalyst B

The same as Example 1, omitting the Nb₂ O₅. An adequately sized, stirredkettle may be used in place of the tumbler of Example 1.

    TABLE I      Butane Air Maleic Anhydride  Ratio Catalyst  Temperature Conc. Thruput     liters  Mol %  Output  g. MA Out.  Example Type ml. dia. Reactor Size     Salt Hot Spot Mol % g/l cat/hr per/min Conv. Sel. Yield g. MA/l.cat. g.     Butane In       1 A 1850 3/16"×3/16" 11/4"×12' 389 421 1.40 87 70 69 67 46 6     8 0.78      388 422 1.45 91 70 69 67 46 71 0.78      392 430 1.63 96     72.1 73 66 48 79 0.82 2 A 1850 3/16"×3/16" 11/4"×12' 395 427     1.43 92.9 75.6 68 67.1 45.8 69.2 0.75 3 B 1850 3/16"×3/16"     11/4"×12' 394 427 1.43 94.9 75.6 68.3 67.1 45.8 73.5 0.77 4  B*     1850 3/16"×3/16" 11/4"×12' 410 421 1.64 107.4 48.0 69.5 60.2     41.9.sup.(1) 75.9 0.71         111.0 48.0 70.2 57.1 40.1.sup.(2) 75.2     0.68     *Same catalyst as B, prepared in larger quantities, same general     procedure.     .sup.(1) 1101 hours on stream.     .sup.(2) 1322 hours on stream.

EXAMPLES 5 AND 6 Reactor

The reactor comprised a 4-tube cylindrical brass block (8" O.D.× 18")reactor made of alloy 360. The block was heated by two 2500 watt (220volt) cartridge heaters controlled by means of a 25 amp. thermoelectricproportional controller with automatic reset. Prior to its insulation,the block was tightly wound with a coil of 3/8" copper tubing. Thisexternal coil was connected to a manifold containing water and airinlets for cooling of the reactor block. The reactors were made of a 304stainless steel tube, 1.315" O.D. and 1.049" I.D., 23-1/2" long,containing a centered 1/8" O.D. stainless steel thermocouple well. Thelower end of the reactor was packed with a 1" bed of 3 mm pyrex beads.The next 12" of the reactor were packed with catalyst (1/8"×1/8" pelletsor 6-12 mesh granules) followed by about a 10" bed of 3 mm pyrex beads.The gas streams are separately metered into a common line entering thetop of the reactor. The reaction vapors are passed through two 2000 ml.gas scrubbing bottles containing 800 ml. of water. The vapors from thescrubbers then go through a wet test meter and are vented. The inletgases are sampled before entering the reactor and after the waterscrubbers. The feed is normally 0.5 to 1.8 mol% C₄, e.g., n-butane, inair, adjusted to maintain a desired temperature. In addition, operatingtemperature can be further controlled by dilution of the air with aninert gas.

The inlet gases and water scrubbed outlet gases were analyzed by gaschromatography using the peak area method. Butane, carbon dioxide andany olefins or diolefins present in the gas streams were determinedusing a 1/4" column with a 5'foresection, containing 13 wt.% vacuum pumpoil on 35/80 mesh chromosorb, followed by a 40' section containing 26wt.% of a 70-30 volume ratio of propylene carbonate to 2,4-dimethylsulfolane on 35/80 mesh chromosorb. The analysis was conductedat room temperature with hydrogen as the carrier gas (100 ml/minute).Carbon monoxide ws analyzed on a 1/4" column with a 3' foresection ofactivated carbon followed by a 6' section of 40/50 mesh 5A molecularsieves. This analysis was run at 35° C. with helium as the carrier gas(20 psi).

The water scrub solutions were combined and diluted to 3000 ml. in avolumetric flask. An aliquot of this solution was titrated with 0.1 Nsodium hydroxide solution to determine maleic acid (first end point) andweak acids in solution and titrated to determine the carbonyls, usinghydroxylamine hydrochloride.

Catalysts' Preparation

The same catalysts were employed in these examples.

The condition of the reactors and the results are reported in Table II.

Butane was extensively employed in the present examples because of itsavailability and easy handling. The other C₄ -C₁₀ hydrocarbons,particularly, normal paraffins and olefins, also are suitable for use inconjunction with the present catalyst to produce anhydrides; forexample, n-pentane, n-hexane, n-heptane, n-octane, n-nonane and n-decaneand the corresponding olefins.

                                      TABLE II                                    __________________________________________________________________________                       Air                                                                  Temp., ° C.                                                                     liters                                                                             Mol %                                                                              GHSV Hrs.On                                                                            Mol % M. A.                                                                          M. A. Output                     Example                                                                            Catalyst                                                                           Block                                                                             Hot Spot                                                                           per min.                                                                           C.sub.4 -Feed                                                                      V/V/H                                                                              Stream                                                                            C S  Y g/lit.cat/hr.                    __________________________________________________________________________    5    A    392 452  7.2  0.636                                                                              2466 791 74                                                                              56 41                                                                              28.4                             6    B    395 452  7.2  0.829                                                                              2439 696 71                                                                              56.1                                                                             40                                                                              35.3                             __________________________________________________________________________

The invention claimed is:
 1. A process for the partial oxidation of C₄to C₁₀ hydrocarbons to the corresponding anhydrides comprisingcontacting a feed of comprising C₄ to C₁₀ alkane hydrocarbons in vaporphase at elevated temperatures, with oxygen and a catalyst compositionconsisting of vanadium, phosphorus and oxygen and a modifying componentcontaining each of Cu, Mo, Ni, Co, Cr, Ce, Nd, Ba, Y and Sm, wherein theatomic ratio of vanadium:phosphorus:modifying component is 1:0.90 to1.3; 0.033 to 0.4.
 2. The process according to claim 1 wherein saidhydrocarbons is a normal hydrocarbon.
 3. The process according to claim2 wherein said normal alkane is n-butane.
 4. The process according toclaim 1 wherein the atomic ratio ofvanadium:phosphorus:Cu:Mo:Ni:Co:Ce:Nd:Cr:Ba:Y:Am is 1:0.90 to 1.3:0.022to 0.201:0.0025 to 0.04:0.0022 to 0.045:0.0040 to 0.066:0.0054 to0.20:0.0022 to 0.2:0.0003 to 0.003:0.0023 to 0.0585:0.0001 to0.02:0.0001 to 0.02, respectively, the total atomic ratio of Cu, Mo, Ni,Co, Ce, Nd, Cr, Ba, Y and Sm being in the range of at least 0.033 to0.4.
 5. The process according to claim 1 wherein said hydrocarboncomprising about 88 to 99 mol percent normal C₄ alkanes and from about 1to 12 mol percent n-butene, benzene or a mixture thereof.